diff --git a/changelog.d/5967.bugfix b/changelog.d/5967.bugfix
new file mode 100644
index 000000000..8d7bf5c2e
--- /dev/null
+++ b/changelog.d/5967.bugfix
@@ -0,0 +1 @@
+Fix list media admin API always returning an error.
diff --git a/synapse/rest/admin/media.py b/synapse/rest/admin/media.py
index f3f63f0be..ed7086d09 100644
--- a/synapse/rest/admin/media.py
+++ b/synapse/rest/admin/media.py
@@ -60,6 +60,7 @@ class ListMediaInRoom(RestServlet):
 
     def __init__(self, hs):
         self.store = hs.get_datastore()
+        self.auth = hs.get_auth()
 
     @defer.inlineCallbacks
     def on_GET(self, request, room_id):